Boxes Stored in Cellars and Garages: The Pest Reservoir Nobody Inspects Before the Holidays

The typical call doesn't come in October. It comes in mid-November, two or three days after a perfectly ordinary errand: "We went down to the basement to fetch the Christmas boxes, we put them in the living room, and ever since there have been brown bugs in the kitchen in the evening." Sometimes it's a variant: "I brought the archives up from the storage unit, and this morning there were droppings on the pantry shelf."

In both cases, the pest didn't invade anything. It was carried in. By hand, inside a box, from a space where it had been living quietly for months — a space nobody ever inspects because you don't sleep or eat there.

Corrugated cardboard is the worst possible storage material in an unheated space: the fluting provides gaps of 3 to 5 mm — exactly the dimension an adult cockroach looks for to wedge itself into — the starch glue binding the sheets is a food source, and damp cellulose is a first-rate nesting material for rodents. A box stored for two years in a Paris-region cellar at 80% relative humidity is no longer a container: it's a habitat.

This article describes what actually lives in the cellars, garages and storage units of the Île-de-France region at this time of year, the signs that let you sort a box without opening it in your living room, the six-step protocol for bringing things upstairs, and the point at which the problem outgrows your own unit and becomes a matter for the building's co-ownership.

Stone Haussmann-style façade with arched windows and a balustraded balcony on a residential building

What really lives in the cellar of a Haussmann-era building

Basements in Paris and the inner suburbs combine three characteristics that turn them into reservoirs: a stable temperature between 12 and 18 °C all year round, relative humidity often above 70%, and a complete absence of foot traffic. No cleaning, no light, no disturbance. Every species finds a niche there.

One point deserves emphasis because it surprises almost all our clients: the Oriental cockroach is a cellar species before it is a kitchen species. In the Île-de-France region we find it in large numbers in the basements of older buildings, in technical rooms and in car parks — and it reaches the occupant by travelling up through ducts, service stairs or, very often, inside a box. Unlike the German cockroach, it tolerates dry heat poorly: once inside a heated flat, it survives in bathrooms and under sinks, rarely anywhere else.

Why October and November concentrate the incidents

Three movements overlap across six weeks.

The thermal movement. With the first nights below 8 °C, rodents look for more temperate quarters. A basement is already an improvement on the outdoors, but a heated flat is better still. The cellar becomes a waiting room.

The human movement. This is the season for hauling boxes upstairs: holiday decorations, winter clothing, tyres, tax archives, ski gear, groceries bought in bulk. The cellar → home flow peaks between mid-October and mid-December.

The moisture movement. The first sustained rains push humidity up in poorly ventilated basements. A box that was dry in August is damp in November: it turns soft, and therefore edible and easy to gnaw through.

It is this convergence that causes a problem established since spring to reveal itself abruptly, in two days, in the most visible room of the home.

Inspect before you carry: the three-minutes-per-box method

The non-negotiable rule: open a box in the storage space, never in the living room. If the contents are contaminated, it's better for the discovery to happen where the pest already lives.

Make sure you have decent lighting — the cellar bulb, where there is one, is not enough to make out 1 mm droppings. A rechargeable head torch leaves both hands free and is the only real comfort in this job; as a supplement, a UV LED lamp reveals rodent urine traces, which fluoresce, along with certain organic stains invisible under white light.

The external check, before opening

• Lower corners and edges: mouse gnawing leaves clean notches 2 to 3 mm wide, often crescent-shaped, on the corners resting on the floor.
• The underside: lift the box. Oriental cockroaches sit underneath objects, not inside them. Brown-black insects 20–25 mm long scattering when exposed to light are a diagnosis in themselves.
• The packing tape: if it has peeled away in places with no human intervention, that means damp or traffic.
• The flutes along the edges: look at the box edge-on. Cockroach moults and droppings accumulate there.
• The floor around it: an accumulation of droppings in a line along a wall indicates a regular route, and therefore a resident population rather than an isolated passage.

The internal check

Open the box flat, without shaking it. Textiles: check the folds and seams. Paper: the edges and the bindings. If you find droppings, moulted skins, egg capsules or shredded paper formed into a nest, the box does not go upstairs. It goes to recycling or the waste centre, its contents are sorted on the spot and transferred into another container.

Façades of Parisian Haussmann-era buildings with wrought-iron balconies under a blue sky

The six-step protocol for bringing things upstairs

1. Sort on the spot. Anything non-essential stays downstairs or goes in the skip. The density of a storage space is the number one risk factor: the fuller it is, the less inspectable it becomes.
2. Transfer, don't transport. Empty the approved contents into brand-new containers. Plastic storage boxes with clip-on lids are not a frivolity: a smooth polypropylene wall is unclimbable for an adult Oriental cockroach and ungnawable for a mouse under normal conditions. They can also be inspected in two seconds, straight through the wall.
3. Treat the textiles. Anything washable goes in at 60 °C. Anything that isn't spends 72 hours in the freezer in a sealed bag at −18 °C — the standard protocol against moth eggs as well as bed bugs. Vacuum storage bags then settle the question of storage, provided they are genuinely airtight and not made of plain non-woven fabric.
4. Vacuum the space. Moulted skins, droppings, cellulose debris: all of it goes. Throw the vacuum bag away immediately, inside a sealed bag, outside the storage space.
5. Monitor for 15 days. Place detection glue traps in the cellar and in the room the boxes passed through. These are indicators, not a treatment: their job is to tell you whether something is moving about, and how fast.
6. Never store food. Dog kibble, bags of rice, cardboard multipacks of bottles, garden bulbs: this is mistake number one in the garage. A 15 kg bag of kibble is a food base that lets a rodent population get through the winter in comfort. Decant into metal or rigid plastic bins with a gasket.

The special case of the garage and the rented storage unit

The individual garage accumulates everything the home refuses: tyres, paint, tools, building materials, moving boxes never opened. Three structural weaknesses add to that.

Up-and-over and sectional doors almost always leave a gap at the side. A 6 mm gap is enough for an adult mouse, which can get through an opening matching the width of its skull. Aged rubber door bottoms crack and come away within three to five years: a rubber garage door bottom seal replaced over one Saturday morning eliminates the most heavily used access route, before any treatment at all.

Electrical conduits and unsealed cable penetrations are the second entry point. Expanding foam alone won't hold: a mouse goes through it in one night. You need stainless steel wool or a metal mesh behind it, then mortar or foam as a finish.

Finally, in rented storage units the party-wall situation is total: you control neither the cleanliness nor the contents of the neighbouring unit. The only real lever is the airtight container, systematically, for everything.

Façade of a Parisian Haussmann-era building with windows and wrought-iron balconies under a blue sky

When it is no longer your problem but the co-ownership's

This is the question that always comes up, and the answer is legally fairly clear. Cellars, car parks, technical rooms, ducts and crawl spaces are common areas. Their upkeep, including rodent and insect control, falls to the association of co-owners, with the managing agent responsible for having the work carried out. Article 14 of the French law of 10 July 1965 entrusts the association with the preservation and administration of the building.

Departmental public health regulations also require owners and managers to keep buildings in a constant state of cleanliness and to ensure that rodents and insects are destroyed there. In Paris, the Paris departmental health regulation restates this obligation, and the Service parisien de santé environnementale (SPSE) can be called upon in cases of clear failure to act. On the rental side, the 2018 ELAN law wrote the absence of pests into the definition of decent housing: a landlord must provide accommodation free of any infestation by pest or parasitic species.

In practice, here is the right sequence:

• Document. Dated photos of droppings, gnawing damage and individual pests. A report without evidence always ends up being left to the neighbours' judgement.
• Write to the managing agent by registered post, requesting a basement survey and a treatment plan. A simple phone call creates no record.
• Ask for a building-wide survey, not a one-off intervention. Treating your cellar without treating the adjoining bin room and the ducts achieves nothing: the population rebuilds itself within a few weeks.
• Have an annual integrated pest management contract added to the general meeting agenda if the problem is recurrent. Two to four visits a year in the common areas cost less than a generalised infestation across twenty units.

What we do not recommend

A few instinctive reactions make the situation worse rather than better.

• Fumigation devices and "shock" aerosols in cellars. They scatter cockroach populations towards neighbouring units and into ducts without reaching the harbourages. You turn a localised focus into a building-wide infestation. ANSES regularly points out that these products, widely used by private individuals, needlessly expose occupants for little effect on established populations.
• Ultrasonic repellents. No robust independent study establishes any lasting effect on rodents, which get used to them within a few days.
• Rodenticide blocks left loose on the floor. They pose a genuine risk to children, pets and non-target wildlife through secondary poisoning. Regulations require secure, locked bait stations, and European biocide rules have progressively restricted private individuals' access to the most potent anticoagulants.
• Sealing up without treating. If you shut a population inside, it will look for another way out — often upwards, and therefore towards the flats.

The correct order is always the same: diagnosis, resource reduction (sorting, food-proofing), treatment, then and only then sealing, then follow-up.

The essentials in eight lines

• Corrugated cardboard stored in a damp environment is not a container, it's a habitat: food, shelter and means of transport.
• Incidents break out between mid-October and mid-December, when boxes travel upstairs at exactly the moment pests are looking for warmth.
• You open and sort in the cellar, never in the home.
• The decisive signs are droppings, moulted skins, egg capsules, crescent-shaped gnaw marks and shredded paper.
• Transferring everything into rigid plastic containers with clip-on lids removes most of the risk on its own.
• No foodstuff, including pet food, should remain in the cellar or garage in its original packaging.
• A 6 mm gap under a garage door is enough for a mouse: the door bottom seal is the first repair to make.
• Cellars, car parks and ducts are common areas: treatment is the managing agent's responsibility, and one building-wide survey is worth more than ten isolated interventions.

If you find fresh droppings, pests active during the day, or damage across several units, the prevention stage is behind you. A professional survey of the basement, with species identification and mapping of entry points, is the only way to stop the building's cellar from feeding the flats all winter long. Our teams, operating 7 days a week across the Île-de-France region, deal with precisely this type of situation, common areas included.